docs: def load_re_from_file(filepath):
      """Converts a re file to Regular Grammar instance"""
      regexp = None
      with open(filepath,'r') as mlfile:
          flagstr = ""
          for line in mlfile:
              cleanline = re.sub("//.*$", "", line)
              if re.search("^\s*$", cleanline):
                  continue
              if re.search ("^#.*$", cleanline):
                  flagstr = cleanline[1:]
                  continue
              if regexp is not None:
                  raise Exception("Regular expression file format error")
              else:
                  regexp = cleanline.rstrip('\n')
      flags = 0
      if "i" in flagstr:
          flags |= re.I
      from pydsl.grammar.definition import RegularExpression
      return RegularExpression(regexp, flags)